The Collaborative Initial Glaucoma Treatment Study (CIGTS), a National Eye Institute supported multicenter clinical trial, provided unique insights to how newly diagnosed open-angle glaucoma (OAG) should be treated, whether by initial surgical or medical intervention. Even so, much clinically-relevant and important information to glaucoma and its treatment remains to be evaluated in the extensive CIGTS data resource. Conduct of the proposed data analyses described in this grant application will provide unique, cost-effective opportunities to investigate additional research questions that are directly relevant to the management and care of patients who have open-angle glaucoma. We propose to conduct extensive analyses that address the following four specific aims: (1) Develop a predictive model that provides a ranking of factors that influence improvement in visual field (VF) during treatment of OAG. (2) Describe the natural history of open-angle glaucoma (OAG) development in initially un-treated fellow eyes, and develop a predictive model for the onset of OAG in such eyes. (3) Investigate VF defects documented in the CIGTS, including their location, cluster number, and extent at baseline, response to IOP reduction and elevation, and the association of baseline VF defect characteristics with the probability of progressive VF loss. (4) Compare alternate methods to define and analyze progressive loss of visual field - pointwise linear regression, mixed linear regression, event-based methods, and trajectory analysis - with regard to the outcomes they yield (risk factors, estimates of VF progression).